ARDS

Acute respiratory distress syndrome (ARDS) is a life-threatening lung condition that prevents enough oxygen from getting to the lungs and into the blood. It is the failure of the pulmonary system to provide sufficient exchange of oxygen to supply the body’s demands. There are around 200,000 cases each year in the US alone, and unfortunately around half of all those who develop ARDS do not survive.

There is a lot of great information on this topic available on ARDSNet, Medscape, PubMed, PubMedHealth, and Wikipedia – ARDS, and UpToDate – ARDS. Here is a great mind map resource for understanding ARDS.

Additionally, I have a page on ARDS, where I have compiled a lot of this information into one source. Here are some of the key points to review.

Berlin Definition

ARDS Pathophysiology

• —Immune and inflammatory responses damage the alveolar capillary membrane
• Hypoxemia
• Increased elastance and decreased compliance
• Increased minute volume requirement
• Increased work of breathing
• Pulmonary hypertension
• —Exudative phase: capillary membrane begins to leak.  Fluid fills the alveoli causing profound impaired gas exchange
• —Acute phase:  movement of fluid multiplies.  This lasts about 4 days with leakage of fluid continuing for about 7 days
• —Appears on chest x-ray as bilateral infiltrates

ARDS

• —Does not affect LV function, and initially PAWP remains below 18.
• —Proliferative phase:  7 to 10 days after onset, and may last up to a month.  Lungs attempt to resolve the inflammation, surfactant production decreased, which causes further damage
• —There is a Ventilation perfusion mismatch and hypoxemia
• —Fibrotic phase:  development of fibrotic tissue in the alveoli, leads to further decreased lung compliance and worsening pulmonary hypertension

ARDS Early Clinical Symptoms

• —Early signs are tachypnea, tachycardia,
• —Dyspnea
• —Rapid shallow respirations
• —Use of accessory muscles
• —Mottling, or cyanosis
• —Breath sounds abnormal
• —Dry Cough
• —Altered loc
• —Confusion
• —Restlessness
• —Retrosternal pain
• —Fever

Diagnostic

• —ABGS ( early hypoxemia, respiratory alkaloses)
• —Chest x-ray
• —CT chest

Management of ARDS

• —Focus on resolving symptoms
• —Anticipate intubation and mechanical ventilation
• —Refractory Hypoxemia:  PaO2 does not respond to increases in FIO2

Ventilation

• —Challenge in ARDS patients is to adequately ventilate while preventing injury to lungs from the high pressures required to inflate noncompliant lungs.
• —Research is ongoing; prevention of ventilator induced lung injury is a major focus currently.
• —Lower tidal volume and permissive hypercapnia results in alveolar hypoventilation
• —Inverse Inspiratory/Expiratory ratio:  Normal ratio is that the inspiratory phase is < expiratory phase.  IVR reverses this so that inspiration takes longer than expiration, protecting the lungs.

Pharmacological Support in ARDS

• —Corticosteroids:  decrease inflammation
• —Vasodilators: Nitric Oxide:  relaxes pulmonary vascular smooth muscle.  Not supported in adults
• —Surfactant:  Not supported in adults
• —Manage fluids conservatively

Here is a great YouTube video synopsis.